Mobile communication systems have been developed to guarantee mobility of users and enable communication for the users. Due to the drastic development of technology, the mobile communication systems provide high-speed data communication service as well as voice communication service.
A future-generation mobile communication system, 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) achieves high-speed packet communication at a data rate of up to 100 Mbps higher than 3GPP data rates. In addition, an LTE-Advanced (LTE-A) system is under discussion, which increases data rates by applying new techniques to the LTE communication system. Hereinbelow, the term “LTE” covers both the legacy LTE system and the LTE-A system.
The LTE standard supports both duplexing modes, Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD). In FDD, different frequency bands are used for an UpLink (UL) and a DownLink (DL), whereas in TDD, the same frequency band is used for a UL and a DL.
One of new techniques to be introduced to the LTE-A system is Carrier Aggregation (CA). In CA, a User Equipment (UE) transmits and receives data in multiple carriers. Specifically, the UE transmits and receives data in a plurality of aggregated carriers (generally, carriers serviced by the same evolved Node B (eNB)). Data transmission and reception of the UE in aggregated carriers is equivalent to data transmission and reception of the UE through a plurality of cells. Therefore, there exists a need for a technique that enables a UE to reliably transmit and receive data to and from an eNB, when CA is applied to TDD cells having different frequency bands and different subframe patterns.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.